As computer cycle times have decreased, Phase Lock Loop (PLL) jitter has become a more important part of the entire timing budget. Traditionally, PLL jitter has been measured in a lab environment using high speed oscilloscopes and related equipment. This means that it is difficult to measure the PLL jitter in an assembled machine and nearly impossible to measure it in a customer's environment. This invention adds jitter measurement capability directly to the PLL circuit, so jitter can be measured during normal operation.